CN112786912A

CN112786912A - Preparation method of porous graphite-based self-humidifying bipolar plate

Info

Publication number: CN112786912A
Application number: CN202110045431.XA
Authority: CN
Inventors: 李晓锦; 苗纪远
Original assignee: Qingdao Hongxuan Hydrogen Energy Equipment Technology Enterprise LP
Current assignee: Qingdao Hongxuan Hydrogen Energy Equipment Technology Enterprise LP
Priority date: 2021-01-14
Filing date: 2021-01-14
Publication date: 2021-05-11

Abstract

The invention discloses a preparation process of a porous graphite-based self-humidifying bipolar plate used as a proton exchange membrane fuel cell. The bipolar plate flow passage area is of a porous structure, and the cooling water of a water flow field in the battery is conducted to the reaction gas side through the micropores under the action of pressure difference so as to humidify the gas. The process comprises the steps of graphite-based mixture, compression molding, high-temperature heat treatment carbonization, electrode plate partial hole sealing and the like. The prepared bipolar plate has higher conductivity and high water permeability, and the conductivity reaches 102-^‑1The water permeability reaches 0.38-2.5ml/min cm²So that the bipolar plate has obvious humidification effect on reaction gas.

Description

Preparation method of porous graphite-based self-humidifying bipolar plate

Technical Field

The invention belongs to the field of fuel cells, and particularly relates to a compression molding and post-treatment method for a self-humidifying bipolar plate.

Background

In proton exchange membrane fuel cells, solid polymer membranes are mostly used as electrolytes for conducting protons, i.e., C-F chain perfluorosulfonic acid membranes (Nafion), such as Nafion-117, 115, 212 series products manufactured by dupont, and the like, and are commercially applied in a large scale. The proton conduction process in the proton exchange membrane is in the form of hydrated protons conducted from the anode to the cathode, and therefore, maintaining sufficient water content of the proton exchange membrane, as an effective carrier for proton conduction, is very important in performing electrochemical reactions on the cathode and anode sides of the cell and in transporting protons. Within a certain range, the proton conduction rate of a proton exchange membrane is proportional to the water content of the membrane, because higher humidification conditions can increase the conductivity of the membrane, thereby increasing the output power of the pile.

Currently, humidification methods include external humidification, internal humidification, and self-humidification. The external humidification is to humidify the reaction gas through a humidifying device independent of the cell body before the reaction gas enters the cell, and the humidifying device can be divided into bubbling humidification, direct liquid water injection, flat membrane humidification or hollow fiber membrane humidification, enthalpy wheel humidification, water vapor injection and the like according to different humidifying principles. The external humidification mode is the most common humidification mode, and has the characteristics of high humidification efficiency, controllable humidification, faster dynamic reaction, good stability and the like, but the defects of complexity, high cost and the like of the whole fuel cell system are caused because a humidifier independent of the cell body is additionally arranged. The internal humidification is to integrate the humidification system with the battery, and the built-in humidifier or 'false battery' with humidification function is used for humidifying the battery, and the function of the internal humidification is to directly introduce water (such as cooling water) into the battery, and the reaction gas and the cooling water are separated by a porous plate, a porous net or a microporous membrane. The cooling water enters the reactant gas channel under the action of the pressure difference and humidifies the reactant gas channel. Internal humidification increases the difficulty of cell assembly and sealing, and water distribution throughout the stack is also uneven, resulting in low humidification levels and slow dynamic response of such humidification. Self-humidification is different from an internal/external humidification mode, does not increase the complexity of a fuel cell system, and has good humidification effect and good reliability and stability. At present, the technical development of self-humidification mainly focuses on two ideas, namely, a diffusion layer, a catalyst layer, a proton exchange membrane and components thereof are optimized or modified, the back diffusion water delivery function of water generated by electrochemical reaction at a cathode side to an anode side is enhanced, the water retention capacity of the anode side is increased, and the anode humidification effect is achieved. The self-humidifying bipolar plate realizes the flowing humidification of the battery reaction gas on a two-dimensional surface and the water permeating and transmitting capacity in the axial direction of the battery by the design of a bipolar plate flow field structure and the porous water permeable characteristic, namely, the water generated at the cathode side or the cooling water in the battery water flow field cavity is strengthened to diffuse and transmit the water to the anode side, thereby having the humidification effect on the anode side.

The porous carbon plate structure contains a plurality of micron-sized pores, and through micropore channels for transferring substances are formed among the pores, so that the porous plate has permeability. The self-humidifying bipolar plate can utilize the permeability characteristic of the porous carbon plate to humidify the cooling water of the water flow field in the battery through the porous carbon plate to the reaction gas side for evaporation under the action of certain pressure difference. US patent 5503944 by UTC discloses a porous carbon plate bipolar plate for fuel cells. The cooling water flows in the flow channel between the two porous carbon plates, enters the anode side under the action of capillary pressure and pressure difference and plays a role in humidifying the anode side. CN1710740A discloses a self-humidifying bipolar plate structure, which humidifies hydrogen and air respectively by micropores communicating a cooling water cavity and a reaction gas flow channel, the micropores are arranged at the inlet of the bipolar plate gas flow channel to control the pressure of the cooling water used for humidification in the bipolar plate, and when the inlet gas flows, the cooling water is sucked into the gas flow channel to humidify the reaction gas. However, the currently disclosed research results all use a porous graphite plate as a base material, and the carving of the flow channel is performed by a machining method, so that the processing efficiency is low, and the preparation method of the porous graphite plate is not researched.

Disclosure of Invention

The invention aims to provide a preparation method of a self-humidifying graphite bipolar plate, which comprises the following main preparation process that a graphite-based composite material is molded through mould pressing, and then the porous self-humidifying graphite bipolar plate is obtained through high-temperature carbonization.

The specific technical measures of the invention are as follows:

(1) preparing materials:

a graphite-based conductive mixture is characterized in that the components of the graphite-based conductive mixture comprise conductive aggregate, adhesive and reinforcing filler, wherein the conductive aggregate is graphite, the adhesive is a composite adhesive mainly comprising modified coal pitch, and the reinforcing filler comprises two-dimensional conductive materials such as graphite fiber and carbon nano tubes; wherein, the conductive aggregate accounts for 40-60 wt%, the adhesive accounts for 10-50wt%, and the reinforcing filler accounts for 5-20 wt%. Weighing and mixing materials according to a formula ratio in a mechanical mixing mode until a uniform mixture is obtained;

(2) compression molding:

putting the mixed materials into a preheated mold for compression molding, wherein the pressure is 25-120MPa, the temperature is 140-;

(3) and (3) high-temperature carbonization pore-forming:

carrying out high-temperature carbonization on the plate subjected to compression molding under the protection of non-oxidizing atmosphere such as N2 or inert gas, heating the plate to 800 ℃ from room temperature, and cooling the plate to room temperature along with the furnace after heat preservation is finished to obtain a porous graphite bipolar plate;

(4) Sealing holes of the polar plate:

and (4) injecting glue and sealing the non-gas flow channel area at the edge of the polar plate to prevent the reaction gas of the polar plate from leaking outwards.

The preparation method of the invention has the following characteristics:

(1) the polar plate has high conductivity and mechanical strength, and the conductivity is 102-333S-cm^-1The bending strength is 22-41 MPa;

(2) the polar plate has high bubble point and high water permeability, the bubble point reaches 0.020-0.025MPa, the water permeability reaches 0.38-2.5ml/min cm2@0.03MPa, and the humidifying effect of the bipolar plate is ensured;

(3) the production process is easy for continuous production, uninterrupted continuous operation mode can be realized by the process steps of material mixing, compression molding, batch high-temperature heat treatment, hole sealing and the like, the production period is short, and the process equipment is simple and is suitable for batch production of bipolar plates;

in conclusion, the technical invention has great practicability.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

Example 1

60wt% of graphite, 10wt% of graphite fiber and 30wt% of modified coal pitch are weighed according to the mass ratio of the composite material component formula, and mixed for 5 minutes. And placing the powder into a die for compression molding, wherein the compression molding pressure is 60MPa, the die temperature is 150 ℃, and the pressure maintaining time is 10 min. And heating the polar plate subjected to compression molding under the protection of Ar atmosphere for carbonization, heating the polar plate to 800 ℃ from room temperature, preserving heat for 1h at the heating rate of 4 ℃/min, cooling the polar plate to room temperature along with the furnace after the heat preservation is finished, and stopping supplying Ar to obtain the porous graphite bipolar plate.

Example 2

Putting 10wt% of graphite fiber into the methylcellulose dispersion liquid to obtain uniformly dispersed slurry, then adding 50wt% of graphite powder and 40wt% of modified coal pitch composite binder, and stirring to obtain uniformly mixed slurry. And casting and leveling the slurry. And cutting the dried thin slices into the sizes meeting the requirements of the die, and laminating the thin slices in the die for compression molding. The mould pressing pressure is 60MPa, the mould temperature is 140 ℃, and the pressure maintaining time is 15 min. And heating and carbonizing the sample subjected to compression molding under the protection of Ar atmosphere, heating from room temperature to 800 ℃, preserving heat for 1h, cooling to room temperature along with the furnace after the heat preservation is finished, and stopping supplying Ar to obtain the porous graphite bipolar plate.

Example 3

Weighing 10wt% of graphite, 50wt% of graphite fiber and 40wt% of modified coal pitch according to the mass ratio of the composite material component formula, and mixing. And placing the powder into a die for compression molding, wherein the compression molding pressure is 20MPa, the die temperature is 130 ℃, and the pressure maintaining time is 30 min. And heating the polar plate subjected to compression molding under the protection of nitrogen atmosphere to carbonize, heating from room temperature to 800 ℃, wherein the heating rate is 4 ℃/min, and cooling to room temperature along with the furnace after the heat preservation is finished to obtain the porous graphite bipolar plate.

Table 1 example bipolar plate water permeability and bubble point

	Water permeability ml/min cm²	Bubble point MPa
			Example 1	0.38	0.020
Example 2	2.5	0.025
			Example 3	0.78	0.025

Claims

1. The self-humidifying bipolar plate is characterized in that a porous graphite-based self-humidifying bipolar plate is obtained by carrying out compression molding, high-temperature heat treatment carbonization and fractional hole sealing on a graphite-based mixture.

2. The graphite-based mixture as claimed in claim 1, which comprises conductive aggregate, binder and reinforcing filler, wherein the conductive aggregate is graphite, the binder is a composite binder mainly composed of modified coal pitch, and the reinforcing filler comprises two-dimensional conductive reinforcing materials such as graphite fiber and carbon nanotube.

3. The graphite-based compound according to claim 1, wherein the conductive aggregate accounts for 40-60 wt%, the binder accounts for 10-30wt%, and the reinforcing filler accounts for 5-20 wt%.

4. The graphite-based compound according to claim 1, wherein the mixing manner comprises mechanical mixing by stirring and slurry mixing by a wet method.

5. Compression molding press according to claim 1, characterized in that the pressure is 25-120MPa, the temperature is 120-190 ℃ and the dwell time is 2-30 minutes.

6. The high-temperature carbonization process as claimed in claim 1, wherein the carbonization temperature is 700 ℃ and 1100 ℃ under the protection of non-oxidizing atmosphere, and the temperature increase rate is 1-10 ℃/min.

7. Partial sealing according to claim 1, characterized in that the areas of the plates to be sealed are impregnated with glue.